Over the last few years, the demand for high speed communication applications has exploded. The Internet, for example, has grown at astronomical rates over the past several years. A significant number of new Internet subscribers connect from a home or a small office using a personal computer (PC). One draw back typically associated with home and small office Internet connection is the relatively slow speeds at which data is transferred between the Internet service provider and the subscriber's PC. The slow data transmission schemes are typically associated with the relatively low bandwidth capabilities of the subscriber line connecting the home or small office to the telephone company.
In order to leverage the existing subscriber loop copper wiring, estimated to have a undepreciated world wide value of $600 billion dollars, new data transmission technologies have been developed. For example, digital subscriber line (xDSL) technologies have been developed to provide high-speed data transmission from the service provider (e.g., the central office (CO) of the telephone company) to the customer premise over the existing twisted-pair copper wiring. Such xDSL technologies leverage modem technology to increase the data transfer bandwidth of the twisted-pair copper wiring. Typically, xDSL modems are provided at the customer premise and at the central office. The modems communicate in accordance with a protocol established by the particular xDSL approach being used.
When the same transmission medium is used for both data and voice transmissions, it is desirable in many instances to use a different frequency band for data transmissions than for voice transmissions. In other words, the data is transferred out-of-band with the voice band. Because different frequencies are used for the voice and data bands, voice and data signals can be concurrently transferred over the common transmission medium. A typical xDSL transmission scheme, for example, transfers the data signals in a frequency band higher than the voice band. Such techniques are sometimes referred to as data over voice transmission schemes. In a typical example, voice signals may be carried in frequency bands below 4 kHz with data signals being carried in frequencies above the voice band, typically from 50 kHz to 1 MHz.
While xDSL technologies may be implemented in a number of different forms, each approach typically uses an xDSL modem at the customer premise which communicates with an xDSL modem at the CO of the telephone company. At the CO, data transmitted over the subscriber line using xDSL technologies is communicated to Internet or other intranet services, for example, over high-speed wide area networks (WAN) service, such as frame relay or ATM services. Different competing forms of digital subscriber line technologies are collectively designated as xDSL technologies with the "x" representing various one or more letter combinations which are used in front of the "DSL" acronym in order to designate the type of technology being used. Some of the more prevalent xDSL technologies include HDSL, ADSL, SDSL and VDSL. A brief discussion of some of the differences between a few examples of xDSL technologies is provided below.
HDSL (High Data-rate Digital Subscriber Line) has been used as a low-cost substitute for T1 lines in symmetrical business-oriented wide area network (WAN) applications. HDSL typically supports 768 kbps full-duplex communication over a single twisted pair, T1-speeds over two twisted pairs, and E2 speeds over 3 pairs. SDSL (Single-line Digital Subscriber Line) is well suited for home use or other small subscriber premise and provides T1 or E1 date transmission speeds over a single twisted-pair copper line. SDSL supports standard voice band transmissions and T1/E1 data band transmission simultaneously over the same line.
ADSL (Asymmetric Digital Subscriber Line) exploits asymmetric upstream and downstream data transmission rates to increase the amount of data which may be delivered to the customer premise. ADSL allocates the larger portion of the bandwidth to downstream traffic. Current ADSL schemes achieve data rates ranging from T1 to 9 Mbps downstream and 16 to 640 kbps upstream. ADSL technologies typically use either carrierless amplitude-phase (CAP) modulation or discrete multitone (DMT) modulation techniques. ADSL technology is especially suited for connecting to a customer premise where, as is often the case in Internet applications, a significantly larger portion of data transfers are provided from the service provider to the customer premise than from the customer premise to the service provider.
The various out-of-band data transmission schemes such as xDSL have provided increased bandwidth for transmitting data to a home or small office over existing subscriber lines. However, when more than one data device is provided within the customer premise, the difficulties and costs associated with connecting the multiple devices together and with providing each device with access to the remote data services such as the Internet increase significantly.